For example, a word line contact region portion in which multiple conductive layers (word lines) are patterned into a staircase configuration has been proposed as a contact structure for connecting the multiple conductive layers to a control circuit in a three-dimensional memory device. An insulating layer is formed on the word line contact region portion; and contact vias pierce the insulating layer and reach the conductive layers of the word line contact region portion. A structure also has been proposed in which air gaps are formed between the multiple conductive layers.